html {
    font-size:62.5% /*~=10px*/
}
body{
    min-width:320px;
    position: relative;
}
@media only screen and (min-width: 401px){
    html {
        font-size: 78% !important;
    }
}
@media only screen and (min-width:481px) {
    html {
        font-size:94%!important
    }
}
@media only screen and (min-width:561px) {
    html {
        font-size:109%!important
    }
}
@media only screen and (min-width:641px) {
    html {
        font-size:125%!important
    }
    body {
        max-width:640px
    }
}